They are characterised by high chromium (19–32%) and molybdenum (up to 5%) and lower nickel contents than austenitic stainless steels. Their mixed microstructure provides improved resistance to chloride stress corrosion cracking in comparison to austenitic stainless steel Types 304 and 316.
Extra strength and improved corrosion resistance comes from the mixed microstructure of austenite and ferrite – usually in a 50/50, but occasionally a 60/40 ratio. They tend to have higher chromium and molybdenum than austenitic stainless steel
Unlike similar steels, duplex also displays improved resistance to localised corrosion, particularly pitting, crevice corrosion and stress corrosion cracking. Due to its ferritic qualities, it also shows very good resistance to stress corrosion cracking when compared to standard austenitic. In some cases, the strength of duplex stainless steel can be up to double that of the most commonly used grades of stainless steel.